cAMP (cyclic adenosine 3',5'-monophosphate) is an important second messenger which participates in relaxing bronchial smooth muscles and regulating functions of inflammatory cells. cAMP is decomposed into inactive 5'-AMP by phosphodiesterase (PDE). Accordingly, if the decompostion by PDE is suppressed to increase intracellular concentrations of cAMP, it is considered that bronchial dilatation and anti-inflammatory effects can be obtained so that concerns have been running high for PDE inhibitors (suppressing decomposition of cAMP) as antiasthmatics. Further, recently, five kinds of PDE isozymes (PDE I, II, III, IV, V) have been identified and their tissue distributions have been revealed (Adv. Second Messenger Phosphoprotein Res., 22, 1 (1988), Trends Pharm., Sci., 11, 150 (1990)).
Among the inhibitors against these isozymes, possibility has been pointed out that the specific inhibitors of PDE IV are effective in treating asthma (Thorax, 26, 512 (1991)). As a compound having the specific inhibition of PDE IV, for example, a compound (rolipram xxx) disclosed in Japanese First (unexamined) Patent Publication No. 50-157360 is known as represented by the following formula: ##STR2##
Although various compounds are known other than the foregoing as disclosed in, such as, Japanese First (unexamined) Patent Publications No. 4-253945 and 5-117239, W09115451, W09207567, EP497564, W09219594, they have not been applied clinically up to date so that development of further useful compounds has been demanded.
In J. Pharm. Sci., 73, 1585 (1984), a compound represented by the following formula and its dopaminergic activity are described: ##STR3##
In Eur. J. Med., 27, 407 (1992), a compound represented by the following formula and its binding affinity at dopamine receptor are described: ##STR4##
In J. Org. Chem., 58, 36 (1993), a compound represented by the following formula is described, while no description about its physiological activity is provided: ##STR5##
In Swiss Patent No. 526535, a compound represented by the following formula is described as a synthetic intermediate: ##STR6##
In Japanese Second (examined) Patent Publication No. 29-16871, a compound represented by the following formula is described as having antiulcer effect: ##STR7##
In Japanese First (unexamined) Patent Publication No. 50-157360, a compound represented by the following general formula is described as a treating medicament for neuropsychosis: ##STR8## wherein R.sup.1 and R.sup.2 independently represent C.sub.1 -C.sub.5 alkyl; R.sup.3 represents hydrogen or methoxy; R.sup.4 represents hydrogen, alkyl, aryl or acyl; and X represents oxygen or sulfur.
In Japanese Second (examined) Patent Publication No. 61-2660, a compound represented by the following general formula is described as a treating medicament for neuropsychosis: ##STR9## wherein R.sup.1 and R.sup.2 may be the same or different and independently represent C.sub.1 -C.sub.5 alkyl; and R.sup.5 represents C.sub.1 -C.sub.8 O-aralkyl, O-aryl, NH-aryl, NH-aralkyl, N-(alkyl).sub.2, N-(aryl).sub.2 or ##STR10##
In Japanese First (unexamined) Patent Publication No. 2-121962, a compound represented by the following formula is described as having calcium antagonism: ##STR11##
In European Patent No. 344577, a compound represented by the following formula is described as a treating medicament for ischemia heart disease: ##STR12##